ISG15 and infection: To rule out a delay in the infection of Isg15−/− MEFs as the cause of reduced actin tail formation and EV release, we analyzed the levels of early (E3) and late (A27 and F13) viral proteins by Western blotting in infected Isg15+/+ and Isg15−/− MEFs (2 PFU/cell) at 9 and 16 hpi.